U.S. patent application number 11/717011 was filed with the patent office on 2007-10-04 for method and device for driving rotating-body, process cartridge, image forming apparatus, and computer program product.
This patent application is currently assigned to RICOH COMPANY, LIMITED. Invention is credited to Yuusuke Ishizaki.
Application Number | 20070229005 11/717011 |
Document ID | / |
Family ID | 38161983 |
Filed Date | 2007-10-04 |
United States Patent
Application |
20070229005 |
Kind Code |
A1 |
Ishizaki; Yuusuke |
October 4, 2007 |
Method and device for driving rotating-body, process cartridge,
image forming apparatus, and computer program product
Abstract
A plurality of detection target portions are arranged around a
rotating shaft of a rotating-body, one of which causes a detector
to generate a first detection signal different from a second
detection signal generated from the others. A first generating unit
generates a reference signal indicating a reference
rotational-position of the rotation-driving source or the
rotating-body before one rotation from a timing of the first
detection signal. A second generating unit reads periodic variation
information from a storage unit based on the reference signal, and
generates a rotation-velocity correction signal for the
rotation-driving source.
Inventors: |
Ishizaki; Yuusuke;
(Kanagawa, JP) |
Correspondence
Address: |
HARNESS, DICKEY & PIERCE, P.L.C.
P.O. BOX 8910
RESTON
VA
20195
US
|
Assignee: |
RICOH COMPANY, LIMITED
|
Family ID: |
38161983 |
Appl. No.: |
11/717011 |
Filed: |
March 13, 2007 |
Current U.S.
Class: |
318/400.03 ;
318/400.05 |
Current CPC
Class: |
G03G 15/5008 20130101;
G03G 15/757 20130101 |
Class at
Publication: |
318/254 |
International
Class: |
H02P 7/06 20060101
H02P007/06 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 15, 2006 |
JP |
2006-070583 |
Claims
1. A device for driving a rotating-body, the device comprising: a
rotation-driving source that outputs a rotation force; a
transmission mechanism that transmits the rotation force of the
rotation-driving source; a rotating-body that is connected to the
transmission mechanism and that is rotated by the rotation force of
the rotation-driving source; a plurality of detection target
portions arranged around a rotating shaft of the rotating-body, one
of the detection target portions causes a first detection signal to
be generated, which is different from a second detection signal
generated from other of the detection target portions; a detector
that detects the detection target portions at a predetermined
rotational-position, and generates the detection signals; a first
reference-signal generating unit that generates a reference signal
for indicating a reference rotational-position of the
rotation-driving source or the rotating-body before one rotation of
the rotation-driving source or the rotating-body from a timing of
the first detection signal; a storage unit that stores periodic
variation information about rotation velocity of the rotating-body
and a measured value of phase information thereof; and a signal
generating unit that reads the periodic variation information from
the storage unit based on the reference signal, and generates a
rotation-velocity correction signal for the rotation-driving
source.
2. The device according to claim 1, wherein the one of detection
target portions has a different shape from that of the other of the
detection target portions, and the detector generates a detection
signal that corresponds to a shape of each of the detection target
portions.
3. The device according to claim 1, wherein a timing when the first
reference-signal generating unit generates the reference signal is
when the detector generates the second detection signal.
4. The device according to claim 3, wherein the other of the
detection target portions are arranged backward in a rotation
direction of the rotating-body next to the one of the detection
target portions.
5. The device according to claim 1, wherein a timing when the first
reference-signal generating unit generates the reference signal is
before the detector detects the other of the detection target
portions arranged backward in the rotation direction of the
rotating-body next to the one of the detection target portions.
6. The device according to claim 1, wherein a plurality of
detectors are prepared, and the first reference-signal generating
unit generates the reference signal based on the first detection
signal that is generated first by the detectors.
7. The device according to claim 1, further comprising: a counter
that counts number of times of detecting the detection target
portions by the detector from a timing when the reference signal is
generated; and a second reference-signal generating unit that
generates a following reference signal based on counted value of
the counter.
8. The device according to claim 7, wherein a total number of the
detection target portions is set at the timing of generating the
reference signal, the total number of the detection target portions
is decremented every time the detection target portion is detected,
and the second reference-signal generating unit generates the
following reference signal when the counted value becomes zero.
9. A process cartridge configured to be mounted on an image forming
apparatus of an electrophotographic system including a
photoconductive drum, the process cartridge comprising the device
according to claim 1.
10. An image forming apparatus comprising the process cartridge
according to claim 10.
11. A device for driving a rotating-body, the device comprising: a
rotation-driving source that outputs a rotation force; a
transmission mechanism that transmits the rotation force of the
rotation-driving source; a rotating-body that is connected to the
transmission mechanism and that is rotated by the rotation force of
the rotation-driving source; a plurality of detection target
portions arranged around a rotating shaft of the rotating-body, one
of the detection target portions causes a first detection signal to
be generated, which is different from a second detection signal
generated from other of the detection target portions; a plurality
of detectors that detect the detection target portions at each
predetermined rotational-position, and generate the detection
signals; a first reference-signal generating unit that generates a
reference signal for indicating a reference rotational-position of
the rotation-driving source or the rotating-body whenever the
rotation-driving source or the rotating-body rotates once based on
a timing of the first detection signal that is generated first by
the detectors; a storage unit that stores periodic variation
information about rotation velocity of the rotating-body and a
measured value of phase information thereof; and a signal
generating unit that reads the periodic variation information from
the storage unit based on the reference signal, and generates a
rotation-velocity correction signal for the rotation-driving
source.
12. The device according to claim 11, further comprising: a counter
that counts number of times of detecting the detection target
portions by the detector from a timing when the reference signal is
generated; and a second reference-signal generating unit that
generates a following reference signal based on counted value of
the counter.
13. The device according to claim 12, wherein a total number of the
detection target portions is set at the timing of generating the
reference signal, the total number of the detection target portions
is decremented every time the detection target portion is detected,
and the second reference-signal generating unit generates the
following reference signal when the counted value becomes zero.
14. A process cartridge configured to be mounted on an image
forming apparatus of an electrophotographic system including a
photoconductive drum, the process cartridge comprising the device
according to claim 11.
15. An image forming apparatus comprising the process cartridge
according to claim 14.
16. A method of driving a rotating-body, the method comprising:
measuring including rotating a rotation-driving source at a fixed
velocity to output a rotation force, supplying the rotation force
to the rotating-body via a transmission mechanism, and measuring
periodic variation of rotation velocity of the rotating-body;
storing measured periodic variation information with reference
rotational-position information of the rotating-body; detecting
including rotating the rotation-driving source at a fixed velocity,
and detecting that one of a plurality of detection target portions
arranged around a rotating shaft of the rotating-body from which a
first detection signal different from a second detection signal
generated from other of the detection target portions is generated
exists at a predetermined rotational-position; first generating
including generating a reference signal for indicating a reference
rotational-position of the rotation-driving source or the
rotating-body before the rotation-driving source or the
rotating-body rotates once after the one of the detection target
portions is detected; and second generating including reading the
periodic variation information based on the reference signal, and
generating a rotation-velocity correction signal for the
rotation-driving source.
17. A computer program product comprising a computer-usable medium
having computer-readable program codes embodied in the medium that
when executed cause a computer to execute the method according to
claim 16.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] The present document incorporates by reference the entire
contents of Japanese priority document, 2006-070583 filed in Japan
on Mar. 15, 2006.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention generally relates to a technology for
driving a rotating-body by transmitting a rotation force from a
rotation-driving source via a rotation-force transmission
mechanism.
[0004] 2. Description of the Related Art
[0005] In an electrophotographic-system image forming apparatus
that forms an image by forming toner images on a surface of a
photoconductive drum and transferring them to a recording sheet,
for example, it is necessary to accurately match peripheral
velocity of a photoconductive drum with a carrier speed of a
recording sheet to transfer toner images formed on a surface of a
photoconductive drum to a recording sheet without change.
[0006] When the photoconductive drum is rotated and driven, for
example, by a DC motor, it is general on account of stabilization
of rotation velocity and securement of a driving torque that the
motor is rotated relatively at high velocity and the rotation
velocity is reduced by decelerating means such as a gear reducer to
drive the photoconductive drum. However, in this event, even if the
motor as a rotation-driving source is rotated at a stable velocity,
periodic variation occurs in rotation velocity of the
photoconductive drum due to a difference in processing accuracy (an
accumulated pitch difference concerning a gear, decentering of a
rotating shaft, and the like) in a rotation force transmission
mechanism that includes a gear. As a result, there is a possibility
that a reproduced image is degraded.
[0007] Therefore, a rotating-body driving device is proposed to
correct this velocity variation that, on condition that a motor is
previously rotated at a certain velocity in shipment of an image
forming apparatus, exchange of a photoconductive drum, or the like,
the rotation force is supplied through a rotation force
transmission mechanism to a rotating-body, and a periodic variation
component in rotation velocity of the rotating-body is measured to
store it in a memory, reads the periodic variation component from
the memory, when using an image forming apparatus, and performs
velocity correction in opposite phase to reduce velocity variation
of the photoconductive drum (see Japanese Patent Application
Laid-open No. 2005-312262).
[0008] As shown in FIG. 24, in the rotating-body driving device, a
disk-shaped detection target body (encoder) 111 that includes a
single slit 114 for detecting a reference rotational-position and a
plurality of slits 113 (4 slits in this case) for detecting the
other rotational positions is mounted around a rotating shaft 112
of a photoconductive drum, and a detector 117 that detects a
rotational position of each of the slits that move along with
rotation of the photoconductive drum is arranged opposite to the
encoder 111. A motor is rotated at a certain velocity and a time
difference of timing at which the detector 117 detects the slits
113 is detected. After a calculation, a periodic variation
component is extracted, as shown in FIG. 25, the component is
stored in a memory by corresponding to timing (home position) at
which the detector 117 detects the slit 114 and then the slit 113.
To correct velocity variation, when detecting the above home
position, a periodic variation component is read from the memory
based on a phase corresponding to the home position and velocity
correction in opposite phase of the periodic variation component is
performed so that, as shown in FIGS. 26A and 26B, periodic
variation in rotation velocity of the photoconductive drum is
controlled.
[0009] However, the slit 114 for detecting a reference
rotational-position is mounted on the encoder 111 separately from
the slits 113 for detecting a time difference in the rotating-body
driving device. Therefore, for example, when the number of slits
113 is increased to enhance accuracy of detecting a time difference
for accurate extraction of a periodic variation component, it is
difficult to provide the slit 114. The slit 114 is a slit only to
detect a home position. Therefore, whenever a slit is detected, it
is necessary to have determination means to determine once, after
the detector 117 detects a slit, whether the slit is for detecting
a home position or for detecting correction data and to store only
the slit that is determined as a slit to detect correction data in
a memory, thereby increasing a load to process software.
[0010] Thus, the applicant of the application proposes a rotation
detecting device that uses a slit that has a larger width for
detection of both a home position and velocity variation by making
one of slits 113 shown in FIG. 24 wider in a peripheral direction
of the encoder 111, identifying passing of the slit that has a
larger width based on a difference of a detection signal from the
detector 117 caused by a difference in a width of a slit, counting
the number of detection of ends of slits 113 in the peripheral
direction (a front end in a rotating direction of the encoder 111)
through the detector 117 from the time point, and detecting an end
of a slit in the peripheral direction with respect to the number of
counting the following slits before detecting the slit 113 that has
a larger width ("4" in FIG. 24) as well as generating a home
position signal (Patent Application No. 2005-266708).
[0011] However, the rotation detecting device identifies passing of
the slit that has a larger width and then generates a first home
position signal after a rotation of the photoconductive drum.
Therefore, until a home position is detected after starting a motor
and the photoconductive drum rotates once, correction of velocity
variation is not started. It is required to reduce time to form a
first copy in an image forming apparatus in view of energy saving
and appliance with respect to a user. It is necessary, to meet the
requirement, to form an image on a photoconductor in a possibly
short time after start of a motor. However, it is impossible for
the rotation detecting device to sufficiently meet the requirement
of reducing time to copy.
SUMMARY OF THE INVENTION
[0012] It is an object of the present invention to at least
partially solve the problems in the conventional technology.
[0013] A device for driving a rotating-body according to one aspect
of the present invention includes a rotation-driving source that
outputs a rotation force; a transmission mechanism that transmits
the rotation force of the rotation-driving source; a rotating-body
that is connected to the transmission mechanism and that is rotated
by the rotation force of the rotation-driving source; a plurality
of detection target portions arranged around a rotating shaft of
the rotating-body, one of which causes a first detection signal to
be generated, which is different from a second detection signal
generated from other of the detection target portions; a detector
that detects the detection target portions at a predetermined
rotational-position, and generates the detection signals; a first
reference-signal generating unit that generates a reference signal
for indicating a reference rotational-position of the
rotation-driving source or the rotating-body before one rotation of
the rotation-driving source or the rotating-body from a timing of
the first detection signal; a storage unit that stores periodic
variation information about rotation velocity of the rotating-body
and a measured value of phase information thereof; and a signal
generating unit that reads the periodic variation information from
the storage unit based on the reference signal, and generates a
rotation-velocity correction signal for the rotation-driving
source.
[0014] A device for driving a rotating-body, according to another
aspect of the present invention includes a rotation-driving source
that outputs a rotation force; a transmission mechanism that
transmits the rotation force of the rotation-driving source; a
rotating-body that is connected to the transmission mechanism and
that is rotated by the rotation force of the rotation-driving
source; a plurality of detection target portions arranged around a
rotating shaft of the rotating-body, one of which causes a first
detection signal to be generated, which is different from a second
detection signal generated from other of the detection target
portions; a plurality of detectors that detect the detection target
portions at each predetermined rotational-position, and generate
the detection signals; a first reference-signal generating unit
that generates a reference signal for indicating a reference
rotational-position of the rotation-driving source or the
rotating-body whenever the rotation-driving source or the
rotating-body rotates once based on a timing of the first detection
signal that is generated first by the detectors; a storage unit
that stores periodic variation information about rotation velocity
of the rotating-body and a measured value of phase information
thereof; and a signal generating unit that reads the periodic
variation information from the storage unit based on the reference
signal, and generates a rotation-velocity correction signal for the
rotation-driving source.
[0015] A method of driving a rotating-body according to still
another aspect of the present invention includes measuring
including rotating a rotation-driving source at a fixed velocity to
output a rotation force, supplying the rotation force to the
rotating-body via a transmission mechanism, and measuring periodic
variation of rotation velocity of the rotating-body; storing
measured periodic variation information with reference
rotational-position information of the rotating-body; detecting
including rotating the rotation-driving source at a fixed velocity,
and detecting that one of a plurality of detection target portions
arranged around a rotating shaft of the rotating-body from which a
first detection signal different from a second detection signal
generated from other of the detection target portions is generated
exists at a predetermined rotational-position; first generating
including generating a reference signal for indicating a reference
rotational-position of the rotation-driving source or the
rotating-body before the rotation-driving source or the
rotating-body rotates once after the one of the detection target
portions is detected; and second generating including reading the
periodic variation information based on the reference signal, and
generating a rotation-velocity correction signal for the
rotation-driving source.
[0016] The above and other objects, features, advantages and
technical and industrial significance of this invention will be
better understood by reading the following detailed description of
presently preferred embodiments of the invention, when considered
in connection with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] FIG. 1 is a schematic view of an image forming apparatus
according to a first embodiment of the present invention;
[0018] FIG. 2 is a schematic side view of a process cartridge in
the image forming apparatus;
[0019] FIG. 3 is a schematic view of a rotating-body driving
device;
[0020] FIG. 4 is a schematic top view of a disk in the
rotating-body driving device;
[0021] FIGS. 5A, 5A', 5B, 5C, and 5D are timing charts for
explaining an operation of generating a home position signal in the
rotating-body driving device;
[0022] FIG. 6 is a flowchart for explaining processing of
generating a home position signal in the rotating-body driving
device;
[0023] FIGS. 7A, 7A', 7B, 7C, and 7D are timing charts for
explaining an operation of generating a home position signal in the
above-proposed rotating-body driving device;
[0024] FIGS. 8A, 8A', 8B, and 8D are timing charts for explaining
an operation of generating a home position signal in the
rotating-body driving device according to a second embodiment of
the present invention;
[0025] FIG. 9 is a flowchart for explaining processing of
generating a home position signal in the rotating-body driving
device;
[0026] FIG. 10 is a timing chart for explaining correction
processing of rotation velocity in the rotating-body driving
device;
[0027] FIG. 11 is a chart for explaining the longest time to detect
a home position in the above-proposed rotating-body driving
device;
[0028] FIG. 12 is a top view for explaining a position of a
detector in the rotating-body driving device according to a third
embodiment of the present invention;
[0029] FIG. 13 is a flowchart for explaining an operation of the
rotating-body driving device;
[0030] FIG. 14 is a chart for explaining the longest time to detect
a home position in the rotating-body driving device;
[0031] FIG. 15 is a flowchart for explaining processing of
generating a home position signal in the rotating-body driving
device;
[0032] FIG. 16 is a top view for explaining a modified example of
arranging a detector in the rotating-body driving device;
[0033] FIG. 17 is a chart for explaining the longest time to
generate a home position signal in the modified example of the
rotating-body driving device;
[0034] FIG. 18 is a flowchart for explaining an operation in the
modified example of the rotating-body driving device;
[0035] FIG. 19 is a flowchart for explaining part of processing of
generating a home position signal in the modified example of the
rotating-body driving device;
[0036] FIG. 20 is a flowchart for explaining part of the rest
processing of generating a home position signal in the modified
example of the rotating-body driving device;
[0037] FIGS. 21A and 21D are charts for explaining the longest time
to generate a home position signal in a conventional rotating-body
driving device;
[0038] FIGS. 22A and 22D are charts for explaining the longest time
to generate a home position signal in the rotating-body driving
device according to a fourth embodiment of the present
invention;
[0039] FIG. 23 is a flowchart for explaining processing of
generating a home position signal in a modified example of the
rotating-body driving device;
[0040] FIG. 24 is a top view for explaining a relation of the disk
and the detector in the conventional rotating-body driving
device;
[0041] FIG. 25 is a chart for explaining periodic variation of
rotation velocity measured and stored in the conventional
rotating-body driving device; and
[0042] FIGS. 26A and 26B are charts for explaining a correction
principle of periodic variation of the rotation velocity in the
conventional rotating-body driving device.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0043] Exemplary embodiments of the present invention will be
explained below in detail with reference to the accompanying
drawings.
[0044] As shown in FIG. 1, an image forming apparatus according to
a first embodiment of the present invention is a color copier that
has 4 sets of image forming subunits, cyan (C), yellow (Y), magenta
(M), and black (B). The image forming apparatus includes a scanner
subunit 2 that performs photoelectric conversion of a light beam
reflected from an exposed duplicated document and processing of
image data on the read document, a writing subunit 3 that
irradiates a photoconductive surface with laser beams that are
modulated based on image data and that are from a laser light
source whose light emission is controlled, and photoconductive
drums 1 whose photoconductive surface is irradiated with laser
beams from the writing subunit 3 and on which an electrostatic
image is formed.
[0045] Around the photoconductive drum 1 are a charging subunit 4
that uniformly charges the photoconductive surface, a developing
subunit 5 that adheres toners on the photoconductive drum 1 on
which a latent image is formed, and a transfer subunit 6 that
transfers a toner image adhered on the photoconductive drum 1 to a
transfer paper (through an intermediate transfer belt). The
developing and forming an image associated with a rotation of the
photoconductive drum 1, here in a tandem system, can be separately
performed for each cyan (C), yellow (Y), magenta (M), and black (K)
component and each color component can be combined in a transfer
process.
[0046] A main unit 7 and a paper feeding bank 8 include a paper
feeding tray. The main unit 7 also includes a manual feeding rack 9
on its side. The color copier includes a belt fixing unit 11 that
supplies heat and pressure to a transfer paper on which an image
has been already formed to fuse toners on the paper, a fixing
roller 12, and a pressure roller 13.
[0047] FIG. 2 is a schematic side view for explaining essential
part of an image forming engine that includes a process
cartridge.
[0048] Image forming units 21C, 21Y, 21M, and 21K that include
charging subunits 4C, 4Y, 4M and 4K (that uniformly charge the
photoconductive surface before optical writing), developing
subunits 5C, 5Y, 5M, and 5K (that develop an electrostatic latent
image generated by optical writing with toners) and cleaning units
15C, 15Y, 15M, and 15K (that cleans residual toners on the
photoconductive drum) are around photoconductive drums 1C, 1Y, 1M,
and 1K respectively. The image forming units 21C, 21Y, 21M, and 21K
serve as a process cartridge that includes the integrated
photoconductive drum 1C, the charging subunit 4C, the developing
subunit 5K, and the cleaning unit 15K, and are detachably attached
to the apparatus body.
[0049] An image is formed on a transfer paper according to the
first embodiment through two transfer processes in which once a
toner image formed on each of photoconductive drums is transferred
to an intermediate transfer belt 19 (a first transfer), and the
image on the intermediate transfer belt 19 is also transferred to a
transfer paper (a second transfer). Image forming is performed
through passing a sheet of paper once so that the images
transferred to the intermediate transfer belt 19 through the
photoconductive drums 1C, 1Y, 1M, and 1K arranged from upstream to
downstream of the intermediate transfer belt 19 on which the images
move with a predetermined distance away among them are superimposed
one another to form a color image, which is then transferred to a
transfer paper. In other words, the toner images that are formed on
the photoconductive drums 1C, 1Y, 1M, and 1K by four colors of
image forming units respectively are first transferred to the
intermediate transfer belt 19 in turn by use of primary transfer
rollers 16C, 16Y, 16M, and 16K. Color-combined toner images first
transferred to the intermediate transfer belt 19 are secondly
transferred to the transfer paper through a secondary transfer
roller 17 and a secondary transfer opposing roller 18 that is
opposite to the secondary transfer roller 17. Toners that remain on
the intermediate transfer belt 19 as a residual toner are removed
by a belt cleaning unit 20.
[0050] An explanation is given about rotation drive control of the
photoconductive drums 1C, 1Y, 1M, and 1K in the color image forming
apparatus according to the first embodiment. A DC brushless motor
is used in the color image forming apparatus shown in FIG. 1 as a
motor for driving each of the photoconductive drums 1C, 1Y, 1M, and
1K and rotation velocity of the motor is reduced by velocity
reduction means such as a gear-type reducer and rotation of the
motor is supplied to the photoconductive drum 1. When each of the
photoconductive drums 1C, 1Y, 1M, and 1K is driven by this motor,
even if the motor as a driving source is rotated at a stable
velocity, periodic variation occurs in rotation velocity of the
photoconductive drum 1 due to a difference in processing accuracy
of a rotation force transmission mechanism that includes a gear (an
accumulated pitch difference concerning a gear, decentering of a
rotating shaft, and the like). As a result, there is a likelihood
of degrading a reproduced image.
[0051] Therefore, the photoconductive drum is rotated as a rotation
body by a rotating-body driving device shown in FIG. 3 so that
periodic variation in rotation velocity of the photoconductive drum
is reduced according to the first embodiment.
[0052] The rotating-body driving device includes a motor 26, a
driving gear 28 connected to the motor 26 through a coupling 27, a
driven gear 29 mated with the driving gear 28, the photoconductive
drum 1 connected to the driven gear 29 through couplings 30, 31, a
disk 32 attached around a rotating shaft 1A of the photoconductive
drum 1, a detector 37 that detects detection target portions 33 to
36 arranged near a peripheral edge of the disk 32, and a controller
38 that receives a sensor detection signal a1 from the detector 37
and also generates a motor driving control signal a2 to control
rotation velocity of the motor 26 based on the received signal to
supply it to the motor 26. The controller 38 includes a central
processing unit (CPU), a read only memory (ROM), a random access
memory (RAM), and an electronically erasable and programmable read
only memory (EEPROM) and determines, described later in detail, a
periodic variation component of rotation velocity of the
photoconductive drum 1 to store it in the EEPROM. When forming an
image, the controller reads the periodic variation component from
the EEPROM and generates a motor driving control signal a2 to
perform velocity correction in opposite phase. The controller 38
also supplies a feedback control signal (not shown) to the motor 26
to rotate it at a certain velocity in response to rotation velocity
information a3 sent from a rotation angular velocity detector (not
shown) of the motor 26.
[0053] As shown in FIG. 4, detection target portions 33 to 36 are
arranged near the edge of the disk 32 at an interval of 90 degrees
in a peripheral direction. The detection target portions 33 to 36
are trapezoidal slits. A length of the detection target portion 33
in the peripheral direction (a length of the detection target
portion 33 in the peripheral direction of the disk 32=a width of
the trapezoid in a radius direction of the disk 32 at the same
position) is longer than a length of the other detection target
portions 34 to 36 in the peripheral direction. The detector 37
includes a light-emitting element and a light-receiving element
that are arranged opposite each other and sandwich the disk 32, or
the light-emitting element and the light-receiving element that are
arranged side by side on one side of the disk 32 to detect the
detection target portions 33 to 36 at a predetermined
rotational-position that move in the peripheral direction of the
disk 32 when the photoconductive drum 1 is driven and rotated by
the motor 26 and the disk 32 rotates. In the case of the opposite
arrangement, the detection target portions 33 to 36 are detected
based on a fact that light beams that are emitted from the
light-emitting element and pass through slits that are detection
target portions 33 to 36 are detected by the light-receiving
element. In the case of the side-by-side arrangement, the detection
target portions 33 to 36 are detected based on a fact that light
beams emitted from the light-emitting element do not reflect on a
surface of the disk 32, pass through slits that are detection
target portions 33 to 36, and are not detected by the
light-receiving element.
[0054] Duration of a detection signal (time from a rising edge to a
falling edge) in either arrangement corresponds to a width of the
slit so that duration of a signal to detect the detection target
portion 33 that has a larger width is longer than that of the other
detection target portions 34 to 36. The detection target portions
34 to 36 and the detector 37 are not limited to a combination of
slits, the light-emitting element, and the light-receiving element
and can be a combination of a magnetic sensor and a magnetic
substance. The detection target portions 34 to 36 are not limited
to a trapezoid in shape and can have a shape that is different in a
length of the peripheral direction at the same radius position of
the disk.
[0055] Operation of the rotating-body driving device that has the
above configuration is explained.
[0056] First of all, prior to correction control to reduce periodic
variation that corresponds to a rotation of the photoconductive
drum 1, velocity variation in a rotation of the photoconductive
drum 1 is detected as correction information for the correction
control to store the velocity variation in the EEPROM of the
controller 38. This processing is performed, for example, in a
manufacturing process before shipment of products or when
exchanging the photoconductive drum 1.
[0057] When performing this processing, the controller 38 outputs
an instruction signal to drive the motor 26 at a target angular
velocity .omega.m and rotates and drives the motor 26. As shown by
an arrow R of FIG. 4, it rotates clockwise. When the controller 38
determines that rotation velocity of the motor 26 reaches a target
rotation velocity based on rotation velocity information a3 output
from the rotation angular velocity detector of the motor 26, the
controller 38 detects a home position of the photoconductive drum 1
and determines velocity variation of rotation of the
photoconductive drum 1 to store it in the EEPROM.
[0058] A procedure of detecting a home position is explained with
reference to a timing chart in FIG. 5 and a flowchart in FIG.
6.
[0059] A waveform detected by the detector 37 when rotating the
photoconductive drum 1 shown in FIG. 3 at a certain velocity is
shown in FIG. 5A. When the detector 37 detects the detection target
portions 33 to 36, an L (low) level is input to the controller 38.
However, on the contrary, an H (high) level can be input to the
controller 38. Inside the controller 38, a falling edge of sensor
input shown in FIG. 5A is detected and a sensor edge signal shown
in FIG. 5A' is generated. After a lapse of a certain time T from a
timing of the sensor edge signal, a home position extracting signal
shown in FIG. 5B is generated. The time T is longer than duration
of the L level in sensor input from the detection target portions
34 to 36 that are not large in width and is shorter than duration
of the L level in sensor input from the detection target portion 33
that is large in width. When the home position extracting signal is
generated and the sensor input is in the L level, the sensor input
is recognized as the detection target portion immediately before
the home position (a reference rotational-position of the
photoconductive drum 1). When detecting a front end of the next
detection target portion in the peripheral direction (falling of
sensor input), a home position signal shown in FIG. 5D is
generated.
[0060] More specifically, a state signal that changes in state, for
example, based on sensor input and a counter of a sensor edge
signal (hereinafter, an edge number counter) are provided and an
initial state of the state signal is regarded as S0, an initial
value of the edge number counter is regarded as 3 that is obtained
by subtracting 1 from the number of all detection target portions
(at step ST1 in FIG. 6). In FIG. 6, "state" indicates a state
signal, "hp_pos" a home position extracting signal (corresponds to
FIG. 5B), "sens_in" sensor input (corresponds to FIG. 5A),
"sens_edge" a sensor edge signal (corresponds to FIG. 5A'), and
"edge_cut" an edge number counter.
[0061] When sensor input is, in generating a home position
extracting signal, in the L level, state is in S1 (Yes at step
ST2.fwdarw.ST3). When a sensor edge signal is detected based on the
state, a home position signal is generated (Yes at step
ST4.fwdarw.ST5).
[0062] State is in S2 based on the next home position extracting
signal (at step ST6) and the number of edges in the following
sensors is counted down (subtract) (at step ST7). Counting-down is
performed when a home position extracting signal is generated. When
the counted value becomes zero after performing count-down (Yes at
step ST8), state is in S1 again after setting the counted value to
3 (step ST9.fwdarw.ST3). When a sensor edge signal is detected in
the state, a home position signal is generated (Yes at step
ST4.fwdarw.ST5). Repetition of this process from this time allows
generation of a home position signal for each rotation of the
photoconductive drum 1.
[0063] The controller 38 generates a home position signal as
described above, determines periodic variation information about
the velocity of rotating the photoconductive drum 1 as shown in
FIG. 25 by measuring spacing in a sensor edge signal or in a home
position extracting signal by use of a timer, and stores the
information in the EEPROM. The determination of the periodic
variation information ends by rotating the photoconductive drum 1
once.
[0064] The controller 38 outputs, when correcting velocity
variation of the photoconductive drum 1, an instruction signal to
drive the motor 26 at a target angular velocity .omega.m and
rotates the motor 26. When the controller 38 determines that the
rotation velocity of the motor reaches the target rotation velocity
based on rotation velocity information a3 output from the angular
velocity detector of the motor 26, the controller detects the home
position of the photoconductive drum 1 and reads a periodic
variation component stored in the EEPROM from a phase corresponding
to the home position, and supplies a motor driving control signal
a2 to the motor 26 to perform velocity correction in opposite phase
of the periodic variation component. As a result, in the same
manner as shown in FIG. 26, periodic variation in the velocity of
rotating the photoconductive drum 1 is controlled.
[0065] The rotating-body driving device according to the first
embodiment is compared with the above-proposed rotating-body
driving device. With regard to the above-proposed rotating-body
driving device, as shown in FIG. 7, after falling of sensor input
with respect to the detection target portion that has a larger
width (a sensor edge at the beginning of FIG. 7A') is detected, the
photoconductive drum rotates once and a home position signal is
generated when falling of sensor input with respect to the
detection target portion that has a larger width (a fifth sensor
edge from the beginning of FIG. 7A') is next detected. With regard
to the rotating-body driving device according to the first
embodiment, after falling of sensor input with respect to the
detection target portion 33 that has a larger width (a sensor edge
at the beginning of FIG. 5A') is detected, the photoconductive drum
rotates by substantially one fourth of its rotation and a home
position signal is generated when falling of sensor input with
respect to the detection target portion 34 that does not have a
larger width (a second sensor edge from the beginning of FIG. 5A')
and that is provided next to the wider detection target portion 33
backward in a rotation direction is next detected, leading to an
earlier timing to start correcting velocity variation of the
photoconductive drum 1.
[0066] Thus, according to the first embodiment, it is possible to
reduce time before starting correction because time to take before
generating a home position signal is 1/4 in the case of the four
detection target portions and 1/n in the case of n-number detection
target portions, compared with the above-proposed rotating-body
driving device that takes a rotation cycle after the detection
target portion 33 that is different in width is detected. As a
result, the rotating-body driving device is applied to a process
cartridge or a photoconductive drum driving part so that it is
possible to respond to a request of reducing time to obtain a first
copy from the image forming apparatus.
[0067] FIG. 8 is a timing chart for explaining an operation of the
rotating-body driving device according to a second embodiment of
the present invention. FIG. 9 is a flowchart for explaining
processing of generating a home position signal. FIG. 10 is a chart
for explaining a waveform of a periodic variation component and
timing for reading. A basic configuration of the rotating-body
driving device according to the second embodiment is the same as in
the first embodiment (FIG. 3). A configuration of performing the
following operation takes less time before starting correction than
in the first embodiment.
[0068] First of all, a home position extracting signal is generated
at the same timing as in the first embodiment (FIG. 8B). When
sensor input of the detection target portion 33 (FIG. 8A) at the
time of generation of a home position extracting signal is in the L
level, it is determined that the photoconductive drum passes a home
position (Yes at step ST11 in FIG. 9) and a home position detecting
signal (FIG. 8D) is generated immediately after the determination
(at step ST12). At that time, a time delay T occurs from a front
end of the detection target portion 33 in the peripheral direction.
With regard to data of detecting a periodic variation component,
the time T is added in the controller 38 to store the data in the
EEPROM.
[0069] In other words, for example, when detection data at the time
of generation of a home position signal is F (t), F (t+T) is stored
as detection data. Thus, the time delay T to determine from an edge
of sensor input to a home position can be corrected. When
correcting periodic variation, a time delay can be corrected by
starting correction of shifting a phase by a time T, as shown in
FIG. 10, based on the result obtained from calculation of detection
data.
[0070] That is, when sinusoidal velocity variation due to
decentering occurs in rotation velocity data at a home position,
the value of velocity variation is .omega.+A sin(.omega.t+.alpha.),
where .omega. is basic angular velocity (angular velocity without
decentering, A is amplitude of velocity variation, and .alpha. is
phase, and velocity variation at a home position is .omega.+A sin
.alpha.. However, when a home position is detected, according to
the second embodiment, velocity variation at the time of generating
a home position is .omega.+A sin(.omega.T+.alpha.), and periodic
variation in rotation velocity can be corrected by using correction
data in opposite phase of the resulting value after detection of
the home position.
[0071] The T is a very short time, compared with a rotation of the
drum (for example, 1/444 of a rotation of the drum in the case of a
rotation of the drum (1.5 Hz: 666 ms), a time of passing the
detection target portion 33 that has a larger width: 2 ms, a time
of passing the detection target portion 34 that does not have a
larger width: 1 ms, and timing of generating a home position
extracting signal: 1.5 ms).
[0072] As described above, according to the first and the second
embodiments, it is necessary to first detect the detection target
portion 33 that has a larger width by the detector 37 and then a
home position when starting correction of periodic variation in
rotation velocity. The presence of only one detection target
portion 33 that has a larger width in a rotation of the
photoconductive drum causes detection of a home position to take
time by about a rotation of the drum at the maximum based on a stop
position of the photoconductive drum before the drum rotating shown
in FIG. 11. The time to detect a home position becomes a big
problem with respect to reduction of correction starting time.
Therefore, according to a third embodiment of the present
invention, plural detectors are provided to detect a home position
by using output of the detector that first detects the detection
target portion that has a larger width and hence the above maximum
time is reduced.
[0073] As shown in FIG. 12, a pair of detectors 37a, 37b are
mounted at positions in which they are opposite each other with the
center of the disk 32 sandwiched therebetween, that is, near both
ends of the disk in a radial direction according to the third
embodiment. As shown in a flowchart of FIG. 13, first of all, a
detection signal from the one detector 37a is used to detect and
store periodic variation data in the same manner as described above
and to generate correction data (at steps ST21 and ST22). Secondly,
a detection signal of the other detector 37b is used to detect and
store periodic variation data and to generate correction data (at
steps ST23 and ST24). When starting correction, the detector that
first detects the detection target portion 33 that has a larger
width in both of two detectors 37a, 37b is regarded as a reference,
and a home position signal and correction data while the detector
is used as a reference are used to correct velocity variation in
the following process. As shown in FIG. 14, this correction enables
time to take from start of rotation of the motor 26 to detection of
a home position to reduce to half of the conventional time at the
maximum, that is, substantially one half of rotation cycle.
[0074] FIG. 15 is a flowchart for explaining processing of
generating a home position signal. In FIG. 15, hp_pos37a, 37b
represent home position extracting signals (that correspond to FIG.
5B) generated based on a sensor edge signal (that corresponds to
FIG. 5A') of the detectors 37a, 37b respectively and sens_in37a,
37b represent sensor input (that corresponds to FIG. 5A) detected
by the detectors 37a, 37b respectively.
[0075] As shown in FIG. 15, the motor 26 starts rotating and an
edge number counter is set to 3 (at step ST31). A home position
extracting signal is generated based on a sensor edge signal of the
detector 37a and it is determined whether sensor input of the
detector 37a is zero at that timing (at step ST32). When the
determination is yes at step ST32, the same processing as
processing that is represented in the timing chart after a lapse of
home position determining time T in FIG. 6 is performed at steps
ST33 to ST38 to generate a home position signal. When the
determination is no at step ST32, the same processing as processing
that is represented in the timing chart after a lapse of home
position determining time T in FIG. 7 is performed at steps ST40 to
ST45 to generate a home position signal. In other words, when the
detector 37a first detects the detection target portion 33 that has
a larger width, steps ST33 to ST38 are performed and when the
detector 37b first detects the detection target portion 33 that has
a larger width, steps ST40 to ST45 are performed.
[0076] In FIG. 12, two detectors 37a, 37b are arranged at the
peripheral edge of the disk 32 with spacing of 180 degrees. When
four detectors 37a, 37b, 37c, and 37d are arranged at the
peripheral edge of the disk 32 with spacing of 90 degrees shown in
FIG. 16, correction can be performed in one fourth of a
conventional time shown in FIG. 17. An addition of another detector
allows starting correction at an earlier time.
[0077] FIG. 18 is a flowchart of processing of generating data when
periodic variation is generated or corrected in FIG. 16. FIGS. 19
and 20 are flowcharts of processing of generating a home position
signal. The same processing in FIG. 18 as in FIG. 13 is given
reference numerals and signs that are used in FIG. 13. The same
processing in FIGS. 19 and 20 as in FIG. 15 is given reference
numerals and signs that are used in FIG. 15. In FIGS. 19 and 20,
hp_pos37c, 37d represent home position extracting signals generated
based on a sensor edge signal in each of detectors 37c, 37d and
sens_in37c, 37d represent sensor input detected by the detectors
37c, 37d respectively.
[0078] As shown in FIG. 18, processing of generating data when
periodic variation is generated or corrected is performed in the
same manner as in FIG. 13 as follows: detecting and storing
periodic variation data of rotation velocity and generating
correction data by using a detection signal of the detector 37a (at
steps ST21 and ST22); detecting and storing periodic variation data
of rotation velocity and generating correction data by using a
detection signal of the detector 37b (at steps ST23 and ST24);
detecting and storing periodic variation data of rotation velocity
and generating correction data by using a detection signal of the
detector 37c (at steps ST25 and ST26); and finally detecting and
storing periodic variation data of rotation velocity and generating
correction data by using a detection signal of the detector 37d (at
steps ST27 and ST28). When starting correction, the detector that
detects a home position the earliest among the four detectors 37a,
37b, 37c, and 37d is regarded as a reference, the home position
signal and correction data are used when the detector is regarded
as a reference to correct velocity variation in the following
process.
[0079] In the processing of generating a home position signal shown
in FIGS. 19 and 20, processing from step ST31 (processing of
starting rotating the motor 26 and setting the edge number counter
to 3) to step ST45 is the same in FIG. 15. Furthermore, a home
position extracting signal is generated based on a sensor edge
signal of the detector 37c and it is determined whether sensor
input of the detector 37c is zero at the timing (at step ST46).
When the determination is yes, the same processing is performed as
processing that is represented in the timing chart after a lapse of
home position determining time T in FIG. 7 at steps ST47 to ST52. A
home position extracting signal is generated based on a sensor edge
signal of the detector 37d and it is determined whether sensor
input of the detector 37d is zero at the timing (at step ST53).
When the determination is yes, the same processing is performed as
processing that is represented in the timing chart after a lapse of
home position determining time T in FIG. 7 at steps ST54 to ST59.
Processing at steps ST47 to ST52 and processing at steps ST54 to
ST59 are the same as at steps ST33 to ST38 in FIG. 15.
[0080] A fourth embodiment of the present invention is a
combination of the first and the third embodiments. The
rotating-body driving device according to the fourth embodiment, in
the same manner as in the third embodiment shown in FIG. 12, is
mounted with the pair of detectors 37a, 37b at positions where they
are opposite each other with the center of the disk 32 sandwiched
therebetween, that is, near both ends of the disk in the radial
direction. When detecting a home position by using output of the
detector that first detects the detection target portion 33 that
has a larger width, in the same manner as in the first embodiment
(FIG. 5), rising of sensor input that corresponds to the detection
target portion 33 that has a larger width is detected and then the
photoconductive drum 1 rotates by substantially one fourth of its
rotation. When falling of sensor input that corresponds to the
detection target portion 34 that does not have a larger width next
to the detection target portion 33 that has a larger width backward
in the rotation direction is detected, a home position signal is
generated.
[0081] Thus, though, in the above-proposed rotating-body driving
device, it takes a two-rotation cycle of the drum at the maximum to
perform from detection of the detection target portion 33 that has
a larger width to generation of a home position signal shown in
FIG. 21, it is possible to start correction by a time of 37.5%
compared with the conventional device because of half of a
rotation+one fourth of a rotation=three fourths of a rotation in
the fourth embodiment shown in FIG. 22.
[0082] A flowchart of processing of generating a home position
signal in this event is indicated in FIG. 23. The motor 26 starts
rotating and the edge number counter is set to "3" shown in FIG. 23
(at step ST61). A home position extracting signal is generated
based on a sensor edge signal of the detector 37a and it is
determined whether sensor input of the detector 37a at the timing
is zero (at step ST62). When the determination is yes at step ST62,
processing of steps ST63 to ST71 is performed to generate a home
position signal. When the determination is no at step ST62,
processing of steps ST73 to ST81 is performed to generate a home
position signal. Processing of steps ST63 to ST71 and steps ST73 to
ST81 is processing of generating a home position signal at the
timing shown in FIG. 5D in the same way as at steps ST1 to ST9 in
FIG. 6.
[0083] Likewise, when the number of detectors is 4 shown in FIG.
16, it is possible to start correction at a time of 25% compared
with the conventional device.
[0084] The present invention according to the above embodiments can
be applied to correction of periodic variation in rotation velocity
that occurs in one rotation cycle of the photoconductive drum 1 and
can be also applied to correction of periodic variation in rotation
velocity that occurs in one rotation cycle of the motor 26. The
periodic variation is mainly caused by transmission difference due
to an accumulated pitch error or decentering concerning teeth of
the driving gear 28. To correct the difference, a detection target
portion that corresponds to one rotation cycle of the driving gear
28 can be mounted on the disk 32 shown in FIG. 4.
[0085] As described above, according to one aspect of the present
invention, after the detector detects the detection target portion
in which a detection signal that is different from that of the
other detection target portion is generated, a reference signal for
indicating a reference rotational-position of the rotating-body or
rotation-driving source prior to one rotation of the rotating-body
or rotation-driving source is generated. Based on the reference
signal, a measured value of the previously stored periodic
variation information is read from a storage unit and a
rotation-velocity correction signal of the rotation-driving source
is generated.
[0086] Furthermore, according to another aspect of the present
invention, after the detector detects the detection target portion
that has a different shape from the other detection target portion,
the reference signal for indicating the reference
rotational-position of the rotating-body or rotation-driving source
prior to one rotation of the rotating-body or rotation-driving
source is generated.
[0087] Moreover, according to still another aspect of the present
invention, after the detector detects the detection target portion
in which a detection signal that is different from that of the
other detection target portion is generated, the reference signal
for indicating the reference rotational-position of the
rotating-body or rotation-driving source prior to one rotation of
the rotating-body or rotation-driving source and when the detector
detects the other detection target portion is generated.
[0088] Furthermore, according to still another aspect of the
present invention, after the detector detects the detection target
portion in which a detection signal that is different from that of
the other detection target portion is generated and when the
detector detects the other detection target portion, the reference
signal for indicating the reference rotational-position of the
rotating-body or rotation-driving source is generated.
[0089] Moreover, according to still another aspect of the present
invention, after the detector detects the detection target portion
in which a detection signal that is different from that of the
other detection target portion is generated and before the detector
detects the other detection target portion, the reference signal
for indicating the reference rotational-position of the
rotating-body or rotation-driving source is generated.
[0090] Furthermore, according to still another aspect of the
present invention, after any one of a plurality of detectors
detects the detection target portion in which a detection signal
different from that of the other detection target portion is
generated, the reference signal for indicating the reference
rotational-position of the rotating-body or rotation-driving source
prior to one rotation of the rotating-body or rotation-driving
source is generated.
[0091] Moreover, according to still another aspect of the present
invention, after any one of the detectors first detects the
detection target portion in which a detection signal different from
that of the other detection target portion is generated, the
reference signal for indicating the reference rotational-position
of the rotating-body or rotation-driving source is generated
whenever the rotating-body or rotation-driving source rotates
once.
[0092] Furthermore, according to still another aspect of the
present invention, based on a signal by which any one of the
detectors first detects the detection target portion in which a
detection signal different from that of the other detection target
portion is generated, the reference signal for indicating the
reference rotational-position of the rotating-body or
rotation-driving source is generated and the number of times by
which the detector detects the detection target portion is counted
based on timing of the reference signal. In response to the counted
value, the following reference signal is generated.
[0093] Moreover, according to still another aspect of the present
invention, the total number of detection target portions is set to
the counter at the timing of the reference signal for indicating
the reference rotational-position of the rotating-body or
rotation-driving source. Whenever the detection target portions are
detected, the number of the detection target portions set in the
counter is reduced. When the value of the counter becomes zero, the
following reference signal is generated.
[0094] Furthermore, according to still another aspect of the
present invention, in the rotating-body driving device that
supplies a rotation force of the rotation-driving source through
the rotation force transmission mechanism to the rotating-body and
also reduces periodic variation of rotation velocity of the
rotating-body based on the previously-stored measured value of the
periodic variation component of rotation velocity of the
rotating-body, it is possible to detect a home position and a
rotation velocity variation component through the same detection
target portion, leading to early detection of a home position. It
is also possible to form an image on the photoconductive drum in a
possibly short time after starting rotation of the rotation-driving
source and sufficiently respond to a request of reducing copying
time.
[0095] Although the invention has been described with respect to a
specific embodiment for a complete and clear disclosure, the
appended claims are not to be thus limited but are to be construed
as embodying all modifications and alternative constructions that
may occur to one skilled in the art that fairly fall within the
basic teaching herein set forth.
* * * * *